Chevy Tahoe Problems - HELP! - PeachParts Mercedes-Benz Forum

gmercoleza · #1 08-18-2006, 10:33 AM

My buddy has a 4WD Tahoe, I'm not sure what year but it's most likely a 1998 to 2003. Has about 90K on the clock. It is exhibiting a few of issues:

Check Engine Light About a month back he had codes read at AutoZone which indicated TPS and one other part which I don't remember, probably MAF. He replaced both, but the TPS light has come back twice. I warned him that generic codes are not necessarily remedied by plug-and-play parts replacement. What are the common failure points?

Dieseling Holy cow, this thing diesels like crazy! Happens when applying heavy throttle while moving. Sounds like an SDL for about a second, then levels out. He runs 87 in it, I believe the manual specifies it. I told him to put 93 in it for a couple of tanks to see if it levels out. It has been 105 here after all. However, shouldn't everything automatically detune if preignition is detected? Maybe his piezoelectric (knock) sensor is blown? But wouldn't that throw a code or invoke limp?

Engine knock When the dieseling levels off, a faint knock can briefly be heard while still under load. Valve train has been ruled out as the noise is not present when revving unsprung and is most apparent under moderate to heavy load. I'm thinking mains or rods? How can that be, when it only has 90K? Is that a known issue on these engines?

As a side point, he is running 5W30 in this vehicle - yikes! This is a severe duty vehicle, often being idled for extended periods in the heat with the A/C on. I don't know what his manual says, but I'm almost certain that 5W30 in an engine with 90K on the clock running in 105* heat is not ideal. I told him to run 15W40 DELO or 20W50 in it. I am not attempting to start another oil thread here (flame suit on), but I do think 5W30 is a little light. Any thoughts?

Mechanically speaking, these Tahoes are supposedly fairly reliable. While Consumer Reports gives thumbs down to the 4WD, it is only due to consistent rollovers in avoidance maneuver testing; the 2WD is actually a "Recommended" vehicle as it exhibits average reliability.

I am aware of the famous piston slap issues plaguing 98 and up GM engines and wonder if some of the engine noise is related. I don't see direct reference to the Tahoe at http://www.pistonslap.com, but I don't exactly know which engine is under his hood either. Is this similar to the BMW alusil issues? Will this engine be seizing shortly?

TIA to all the experts...

gmercoleza · #2 08-18-2006, 11:45 AM

I considered the EGR, but I'm pretty certain EGR will throw a code. Besides, in my experience EGR related issues tend to manifest themselves as pinging under light throttle, low RPM while cruising on the highway.

But you might be on to something. Testing with a MityVac is probably in order. It might be beneficial for him to try cleaning the EGR out. Also maybe running some water or top end cleaner into the engine several times and letting it sit overnight each time. I successfully cured pinging in my Dad's Volvo a few weeks back using this method. After reviewing some more info on the GM piston slap issue, there could be top-end buildup that is causing the preignition. Who knows - this could also be throwing the CEL?

rwthomas1 · #3 08-18-2006, 01:08 PM

In Texas heat I would say a 10W-40 or 15W-40 far more appropriate for a GM V8 with 90K on it. When was the last time the spark plugs were changed and are they the correct plug? Incorrect plugs can cause all sorts of strange knocking/pinging if they are to hot in the heat range. I would be tempted to change the oil and the plugs and then tow at least 5,000lbs around for at least 100miles. The hot/hard pulling usually blows out carbon, etc. that accumulates from light use. RT

gmercoleza · #4 08-18-2006, 01:19 PM

Not sure about the plugs. I'm guessing with 90K maybe it's never been tuned up yet. You are right though - I am reminded of an old Dodge Van with the bulletproof slant-6 I used to have that would detonate and sometimes continued running even after you shut it off. Pulled the plugs and they were the wrong heat range. Were probably glowing red hot and preigniting the A/F mixture.

I emailed this thread to the owner, so he is monitoring it.

I told him to try cleaning the top end, test the O2 duty cycle, run Techron or Chevron 93 through the gas tank, even check compression and EGR since these are all cheap or free.

Thanks for the suggestions, please keep 'em coming!

gmercoleza · #5 08-20-2006, 09:56 AM

Bump - Ttt

TheDon · #6 08-20-2006, 10:47 AM

bring it in and tell gm.. its slapping and make them dissasemble the engine and inspect it . on their bill

Gil · #7 08-20-2006, 11:27 AM

Not that this helps your buddy much, but do yourself a favor and take Consumer Reports with a BIG grain of salt. After the way they targeted Suzuki a few years back I wouldn't always trust their conclusions.

Why? They deliberately rolled a Samurai during very unrealistic testing while ignoring easier rollovers from other vehicles like the Ford Bronco II. Consumer Reports (Consumer's Union) had just spent millions on their new corporate headquarters and was looking for a soul to steal to help pay for it. Suzuki had cash, but not so much cash and political influence as to be better protected from stupid lawsuits. Consumer's Union stood to gain a piece of the profits from any suits against Suzuki (under a certain legal doctrine I won't bore you with). So, they publish a scare tactic safety report, get people who think they're affected to sue Suzuki, collect their share of the profits and look like heroes in the process. The American way. But I digress...

Maybe what they said about the 4wd Tahoe was true, but after the Samurai debacle I have to wonder under what circumstances they got it to roll.